For example, it is important to form an Si based thin film having a high quality at a high speed in order to reduce a manufacturing cost in a manufacture of a thin film Si based solar cell. A method of forming the Si based thin film at a comparative low temperature of a substrate which is equal to or higher than 100° C. and is equal to or lower than 400° C. is roughly divided into a plasma CVD (Chemical Vapor Deposition) method and a thermal catalyst CVD method (including a method having an identical principle, for example, an HW (Hot Wire)-CVD method or the like).
The plasma CVD method uses a plasma, thereby damaging a deposited film by charged particles, such as ions and electrons. For this reason, there is a fear that a film quality of a deposited film might be degraded.
On the other hand, the thermal catalyst CVD method does not use the plasma. Therefore, it is possible to form a deposited film at a high speed comparatively easily without damaging the deposited film due to charged particles in principle. However, an excessive decomposition of a material gas (for example, an SiH4 gas) is caused by a heated catalyzer which is heated to a high temperature so that a generation of SiH2, SiH and Si causing a degradation in a film quality progresses. For this reason, the film quality obtained by the thermal catalyst CVD method is lower than the film quality obtained by the plasma CVD method.
For the problems, the applicant has proposed a gas separation type plasma CVD apparatus in which advantages of the plasma CVD method and the thermal catalyst CVD method are combined (for example, see Japanese Patent Application Laid-Open No. 2003-173980).
According to the apparatus, a material gas having a low decomposition probability, for example, an H2 gas can be introduced into a chamber while decomposing and activating an H2 gas via a gas supply path in which a mechanism for enhancing a decomposition probability represented by a heated catalyzer is provided.
Therefore, it is possible to cause the H2 gas to contribute to a formation of a microcrystalline silicon film without increasing charged particles which degrade the film quality that is a problem in the plasma CVD method. In addition, a material gas having a high decomposition probability such as the SiH4 gas is introduced into a chamber via another gas supply path in which a heated catalyzer is not provided. Therefore, it is possible to cause the SiH4 gas to contribute to a formation of a deposited film while suppressing the generation of SiH2, SiH and Si which degrade the film quality in the thermal catalyst CVD method. As a result, the gas separation type plasma CVD apparatus can form a film having a high quality at a high speed.